Periodic Reporting for period 1 - VIROME (Shaping of long term innate immunity by viral education of bone marrow monocytes)
Reporting period: 2020-01-01 to 2021-06-30
MuHV-4 and PVM models have been used to perform a high resolution phenotypic characterization of virus-imprinted monocytes. Indeed, monocytes isolated from bone marrow, blood and lung of mock or virus-infected mice have been profiled by flow cytometry at different times post-infection, as well as monocyte progenitors. This classical immunophenotyping has revealed specific functional properties and distinct activation states between the two models of infection. In addition, a transcriptomic profiling by single-cell RNA sequencing has been done in the context of MuHV-4 acute infection revealing key regulatory features.
WP2: Investigation of the mechanisms underlying initial priming of monocytes
In this part of the project, we investigate the initiating steps leading to monocyte priming. In particular, we are studying the role of resident CD169+ bone marrow macrophages in monocyte early education during viral infection. Interestingly, we observed important phenotypic alterations of these bone marrow macrophages after infection such as overexpression of MHCI and MHCII molecules but also increased expression of cytokines and chemokines, suggesting the existence of a biological crosstalk between these macrophages and other immune cells. Importantly, by using CD169 DTR transgenic mice allowing the inducible depletion of these macrophages, we observed the ablation of bone marrow CD169+ macrophages skews the monocyte phenotype towards an inflammatory profile, associated with viral disease exacerbation. RNA sequencing of those bone marrow macrophages has been done and are currently under analysis. These data will improve our understanding of the biology of bone marrow CD169+ macrophages upon viral infection and will also designed relevant target useful to generate a new transgenic mouse model allowing a more specific depletion of these cells.
WP3: Investigation of the functional outcomes of monocyte imprinting for the host immunity.
3.1. Investigation of the consequences of monocyte imprinting for the primary anti-viral response
Here, we studied the importance of monocyte for the MuHV-4 lifecycle. As stated above, monocytes are pleiotropic cells contributing to the overall orchestration of immunity. Understanding the balance between pro-inflammatory and immunomodulatory pathways triggered by monocytes upon viral infections is of major importance since mechanisms underlying deleterious inflammation induced by highly pathogenic respiratory viruses, are not well known yet. In this WP, we highlighted that pulmonary infection with MuHV-4 induces the early recruitment of CCR2+ monocytes in the airways that finely control the host immune response. More precisely, we uncovered that MuHV-4 imprinted monocytes cluster CD4 T cells in their vicinity and promote a regulatory crosstalk through immune checkpoint proteins. These results revealed a new role for virus-imprinted monocytes in shaping the functional profile of effectors CD4 T cells and identified a key pathway that could be targeted by therapeutic strategies aiming at dampening the host hyperinflammation. This work has been submitted for publication.
3.2. Investigation of the consequences of monocyte imprinting for long-term lung immunity
Here, we are investigating how viral infections affect the alveolar landscape and what are mechanisms driving the long-term persistence of monocyte-derived alveolar macrophages. Indeed, while alveolar niche depletion is a common consequence to different inflammatory insults, only some specific contexts allow the lasting engraftment of monocyte-derived cells. Using partial bone marrow chimeras and complementary fate-mapping models, we observed significant differences in the alveolar niche replenishment during distinct viral infections. Viral imprinting of the alveolar landscape has further consequences on heterologous responses such as the development of allergic asthma. As such, we demonstrated that MuHV-4 reprograms the alveolar macrophage niche for the long-term by dampening type 2 properties of group 2 innate lymphoid cells (Study in revision in Science Immunology). Besides, we also highlighted the protection conferred by gammaherpesvirus imprinting against unrelated viral infections, such as pneumovirus challenges (Publication accepted in March 2020 in Mucosal Immunology, https://doi.org/10.1038/s41385-020-0293-7). We are now deciphering the mechanisms underlying these cross-protective effects.
3.3. Investigation of the consequences of monocyte imprinting for long-term lung immunity
Beyond the respiratory tract, monocyte viral imprinting could shape immune response organs that are not directly targeted by the primary infections. In particular, since monocytes constantly contribute to the pool of intestinal macrophages, we are interested in studying importance of the history of viral infection for the development of individual susceptibility to inflammatory intestinal diseases as well as the potential underlying mechanisms.